On Nov. 1, NASA’s Lucy spacecraft will introduce humans to a world called Dinkinesh — nicknamed Dinky — the smallest main-belt asteroid we’ve ever seen up close.
Lucy launched in 2021 to explore a mysterious group of asteroids called Jupiter’s Trojans. These space rocks orbit the Sun at the same distance as Jupiter in two clusters: one cluster races ahead of the gas giant, while the other sticks behind the planet. All told, scientists know of more than 12,000 of these objects in Jupiter’s orbit, and they believe that this eclectic group of primitive space rocks could help decode the early history of the solar system. Therefore, Lucy will pass by six of Jupiter’s Trojans in early 2027.
“The goal of Lucy is to understand the diversity of Trojan horses,” says Hal Levison, a planetary scientist at the Southwest Research Institute in Colorado and principal investigator of the Lucy mission. “To do that, you have to visit a lot of properties, which is what we do, and to do that, you have to drag your ass.”
Lucy is moving so fast that the mission’s primary science observations are just 24 hours spread over the spacecraft’s 12-year trip around the solar system, Levison says. The mission just flies past its targets, doesn’t make long stays – and once the probe leaves the asteroid, that’s it. “There is no going back; there are no upheavals,” he says.
So when mission personnel realized that as Lucy traveled through the outer solar system, she would fly within 40,000 miles of a small, then-unnamed asteroid, they decided to go for a dress rehearsal and nudged the mission’s trajectory so that it would pass just 280 miles from the tiny asteroid. body. Since Dinkinesh aligned with the Sun and the spacecraft during the flyby, the maneuver will better mimic future planned Trojan flybys than the mission’s original first target, another main belt asteroid that Lucy is scheduled to encounter in 2025.
(The Lucy mission is named after an ancient hominin fossil found in northern Ethiopia that suggested early human relatives walked on two legs about 3.2 million years ago; the fossil is called Dinkinesh in Amharic. The spacecraft’s 2025 destination, the asteroid Donaldjohanson , is named after the paleoanthropologist who led the excavations that uncovered Lucy in 1974.)
Besides, Lucy’s science team has more reason to worry about the flybys than they would have hoped. In the months following Lucy’s launch, the spacecraft’s personnel struggled to fully deploy one of the probe’s two circular solar arrays before finally concluding that the mission was OK to proceed to fully lock the array in place. The probe’s good performance during a flyby of Earth last fall confirmed that decision, but the unreleased field could cause the probe — and its instruments — to shake more than planned during flyby observations, potentially reducing the quality of Lucy’s data. Testing the progress on Dinkinesh will give the team enough time to adjust the probe’s approach to each Trojan target as needed to ensure sharp images and measurements.
So for Lucy, Dinkinesh is primarily an engineering test and practice run. But planetary scientists — who never turn down an opportunity to see something new in the Solar System — are thrilled with their sight of a tiny space rock.
“The science is a bonus, but the bonus science is always really interesting in my experience,” says Jessica Sunshine, a planetary scientist at the University of Maryland and co-investigator of Lucy. “Together, in planetary science, we’ve never flown by an object and thought, ‘Eh, well, that was pretty boring.’
When Dinkinesh was formally added to Lucy’s itinerary earlier this year, scientists only knew its location and bland size. “We knew it was a little small — but nothing else really,” says Julia de León, a planetary scientist at the Institute of Astrophysics in the Canary Islands who is not on the Lucy mission but helped coordinate some of Dinkinesh’s preparatory inspections. “So we all did our best,” he says, as astronomers rush to telescopes to learn more about the asteroid.
Thanks to these efforts, scientists now have a slightly better picture of Dinkinesh, which is shaping up to be an interesting little space rock: silica-rich, roughly elongated, and steadily rotating, with an estimated diameter of about 900 meters and about twice a day. the length of Earth’s 24-hour daily period.
In the main asteroid belt between Mars and Jupiter, scientists have visited only much larger space rocks such as the Dawn mission targets, the asteroid Vesta and the dwarf planet Ceres, which are among the largest known objects in the belt. Both are hundreds of times larger than Dinkinesh. “It’s by far the smallest we’ve ever seen in the main strip,” Sunshine says of Lucy’s little goal.
However, Dinkinesh appears to be similar in size to several near-Earth asteroids that spacecraft have seen up close recently. These include carbon-rich Bennu, samples recently delivered to Earth by NASA’s OSIRIS-REx mission, as well as Didymos, which NASA’s Double Asteroid Redirection Test (DART) mission passed on its way to impacting the small asteroid moon Dimorphos.
Comparing Dinkinesh and Didymos should be particularly interesting, Sunshine says, because the two asteroids are made of the same type of material and are similar in size, just in different locations. “It’s rare that we have such a direct comparison in our science lineage, so I was very excited when it became a clear flyby target for Lucy,” she says.
Such a direct comparison is particularly valuable because scientists believe that near-Earth asteroids originate from the main belt, having been ejected deeper into the solar system by past gravitational perturbations. So scientists hope that Lucy’s view of Dinkinesh will help them understand the changes that main belt asteroids go through as they transform into near-Earth asteroids. “It will be like studying a near-Earth asteroid in its source region, where it is generated,” says de León.
Lucy’s flyby of Dinkinesh will solidify scientists’ preliminary estimates of the asteroid’s basic shape and composition, as well as allow them to count craters on its surface to better calibrate its age. And aside from specific scientific questions, asteroid experts are excited to see another of the Solar System’s space rocks grab the spotlight.
“It’s going to be amazing to see these (images) come down,” says Sunshine. “It does not age; I’ll tell you that much.”
